1. Field of Invention
This invention relates generally to an improved structural member, and more particularly, to a structural member having a non-planar web. Still more particularly, the present invention relates to a sinusoidal structural support beam for aircraft and other lightweight, high-strength applications.
2. Description of Prior Art
In the aircraft industry, it is common to utilize I-beam like structural members having a sinusoidal web extending normally between a top and bottom flange. The generally sinusoidal shape of the web provides increased strength to weight performance, improved stiffness, and decreased volume. In order to accommodate the aircraft wiring harness, hydraulic and fuel lines, as well as immediate strength and volume requirements, the geometry of the web may vary from sinusoidal to planar, creating a potentially non-repeating web corrugation pattern.
Currently, structural members are generally constructed from metal or composite materials. With either choice of material, the construction of a structural member with a sinusoidal web is a challenge, in maintaining quality, tolerances, and minimizing costs. With the high cost of manufacturing composite structural members, due to the labor intensive techniques utilized, it is at times more economical and practical to use metals, such as titanium and aluminum, to construct sinusoidal structural members, when the design allows for it.
Because the sinusoidal web structural member cannot be extruded, like common I-beams, the web and flanges generally must be constructed as separate parts, and then attached, with the web communicating normally between the upper and lower flange. When using metal, it is a common practice to weld or fuse the flanges to the web. The welding device can be TIG, arc, plasma, laser, electron beam or any other effective fusing device. Other methods, using fusing materials such as solder and epoxy are also utilized.
To construct the sinusoidal web, it is common to use a roll former or other similar device to create the desired corrugated pattern. Certain materials, such as titanium alloy 6-4, have considerable spring-back properties, making them relatively difficult to roll form to the tight tolerances required in the aerospace industry. Because the structural integrity, stability, and fit of the sinusoidal beam rely on maintaining the proper tolerance, it is important to implement a method or device to forcibly compress the sinusoidal web into compliance. This is commonly achieved through a clamping means.
In certain industries, such as construction, sinusoidal or trapezoidal structural beams are also utilized. One such beam disclosed in U.S. Pat. No. 6,415,577 to Curtis, describes a generally trapezoidal web extending between an upper and lower rectangular tube. The web is fastened, welded, or otherwise fused to the flange surface contacting the web edge, on both the upper and lower flange. The weld bead lies in the corner formed between the flange and web surfaces. This weld bead can be either continuous along the entire length of the beam or intermittent. With this method, it is difficult to maintain the dimensional tolerances required for the aviation industry. Because the welder requires access to the entire length of the beam, a comprehensive rigid clamping means to maintain tight tolerances may not be practical, due to interference between the clamping means and the welding device.
It is also a common practice in industry to utilize a clamping means to maintain the desired tolerance, while welding from the outer surface of the flange, through the flange, and into the top edge of the sinusoidal web, for both the upper and lower flanges. This manufacturing technique accommodates the tight tolerancing required for many aerospace and high technology applications. However, while holding the web and flanges firmly in place, the clamping means tends to block off access to the web and inner surfaces of the upper and lower flanges. Therefore, the only surface exposed to the welding device is the outer surface of the flange. Because the sinusoidal shape of the web edge is not entirely visible or accessible while secured in the clamping fixture, the weld must be created solely on the expected position of the web edge at any given point, and not necessarily the actual position, creating a blind weld situation. When dealing with the thin gauge metal required for lightweight applications, it is difficult to guarantee that the weld bead will fully penetrate the flange and the sinusoidal web edge at every given point along the length of the beam, using this blind method. Even when using a computer programmed path for the welding device, it is difficult and costly to produce the required bond between the flange and web, due to the slightly unpredictable nature of sinusoidally formed sheet metal webbing. Also, the clamping means cannot be in close contact with the weld area to maintain the position of the web, for fear of interfering with the weld.
What is needed is an economical sinusoidal structural beam and manufacturing method that can maintain the tight tolerances required for items such as wing spars and floor beams in aerospace and other high strength, low weight applications.